Death of a massive star and birth of compact neutron star binary

The research was led by graduate student Kishalay De and is described in a paper appearing in the October 12 issue of the journal Science. The work was done primarily in the laboratory of Mansi Kasliwal (MS '07, PhD '11), assistant professor of astronomy. Kasliwal is the principal investigator of the Caltech-led Global Relay of Observatories Watching Transients Happen (GROWTH) project.

When a massive star -- at least eight times the mass of the sun -- runs out of fuel to burn in its core, the core collapses inwards upon itself and then rebounds outward in a powerful explosion called a supernova. After the explosion, all of the star's outer layers have been blasted away, leaving behind a dense neutron star -- about the size of a small city but containing more mass than the sun. A teaspoon of a neutron star would weigh as much as a mountain.

Supernova - Star - Blasts - Material - Outer

During a supernova, the dying star blasts away all of the material in its outer layers. Usually, this is a few times the mass of the sun. However, the event that Kasliwal and her colleagues observed, dubbed iPTF 14gqr, ejected matter only one fifth of the mass of the sun.

"We saw this massive star's core collapse, but we saw remarkably little mass ejected," Kasliwal says. "We call this an ultra-stripped envelope supernova and it has long been predicted that they exist. This is the first time we have convincingly seen core collapse of a massive star that is so devoid of matter."

Fact - Star - Implies - Lots - Material

The fact that the star exploded at all implies that it must have previously been enveloped in lots of material, or its core would never have become heavy enough to collapse. But where, then, was the missing mass?

The researchers inferred that the mass must have been stolen -- the star must have...